Biology subjects

O'Neill, K. M.

Publications and source records attributed to O'Neill, K. M..

7 recordsLinked to original sources

bioRxiv2025

Nanotopographic Control of Actin Waves and Growth Cone Navigation in Developing Neurons

The development of axons and dendrites (neurites) in a neural circuit relies on the dynamic interplay of cytoskeletal components, especially actin, and the integration of diverse environmental cues. Building on prior findings that actin dynamics can serve as a primary sensor of physical guidance cues, this work investigates the role of nanotopography in modulating and guiding actin waves and neurite-tip dynamics during early neural circuit development. Although actin dynamics is well known to contribute to pathfinding in wide axonal tips, typically referred to as growth cones, we also observe dynamic actin remodeling throughout neurites and at other, narrower, neurite tips. We find that actin-wave speeds do not change significantly in the first two weeks of neurite development on flat substrates, but decrease over the same period in neurites on nanoridges. The ability of nanoridges to guide actin waves and the neurite-tip direction also decreases as neurites mature, both for narrow tips and wide growth cones. This change in responsiveness to physical guidance cues with neuronal maturation may impact the regenerative capacity of developing neural cells that are inserted into mature brains.

biophysics↗

bioRxiv2025

Collective Learning in Living Neural Networks Facilitated by Contextual Background Photostimulation

This study explores collective learning in living neural networks, focusing on group-to-group Hebbian learning, i.e., strengthening and weakening of links dependent on the precise timing of their activities. While neuronal plasticity is now well understood for single pairs of neurons, recent research has demonstrated that groups of tens of neurons are required to encode information in mammalian brains. Thus, it is critical to understand how mechanisms of plasticity, in particular spike-timing-dependent plasticity (STDP) operate at the group scale. We find that neuronal groups can reach significant plasticity after only 45 stimuli when a proper tradeoff between pulse duration and photostimulation effectiveness is chosen. Background stimulation, which enhances the reliability of response for the targeted neuronal groups, is necessary for rapid network-level Hebbian learning. By demonstrating enhanced learning in the presence of background activity, this study underscores the highly cooperative character of neurons and the importance of investigating learning, information flow, and memory formation at the network scale.

neuroscience↗

bioRxiv2023

Collective Information and Communication in Morphologically Distinct Astrocytes

The discovery that astrocytes are an active, rather than a passive, component of the brain has ushered in a paradigm shift in thinking about how the brain processes information. Although the mechanisms by which astrocytes integrate information from neurons are still debated, such discourse should not distract from the importance of more completely understanding how astrocytes communicate via signals amongst themselves. This work aims to study how different astrocytes signal within their own networks. We investigate group calcium (Ca2+) dynamics in polygonal, stellate, and reactive astrocytes. These distinct and important astrocyte subtypes are present in the brain to varying degrees at different physiological states. We use an information-theoretic framework to quantify the dynamics embedded in the Ca2+ traces within astrocyte networks; specifically, we employ the Hurst exponent, cross-correlation, mutual information, and partitioned entropy to assess differences in the astrocyte signals across subtypes. To gain insights into the ability of astrocyte networks to respond to changes in the extracellular environment, we probe the networks with perturbations affecting their cytoskeletal dynamics (Latrunculin B) and energetic levels (Adenosine triphosphate). Overall, these three classes of astrocytes behave differently and respond idiosyncratically to their extracellular environment. We find that polygonal astrocytes are not quiescent, stellate astrocytes respond most strongly to ATP, and reactive astrocytes are uniquely perturbed by Latrunculin B. Interestingly, despite these distinct differences in behaviors, we find a uniform speed of information transport regardless of subtype or perturbation; this uniformity is maintained when using both cross-correlation and mutual information to assess this speed. We conclude that the differential ways astrocytes signal within our measured framework yield important insights into how astrocytes communicate and contribute to this pressing issue of understanding astrocyte information processing.

biophysics↗

bioRxiv2023

Coupled Biomechanical and Ionic Excitability in Developing Neural Cell Networks

Waves and oscillations play a key role in the flow and processing of information in the brain. Recent work has demonstrated that in addition to electrical activity, biomechanical signaling can also be excitable and thus capable of self-sustaining oscillations and waves. Here we measured the biomechanical dynamics of actin polymerization in neural precursor cells throughout their differentiation into populations of neurons and astrocytes. Fluorescence-based live-cell imaging allowed us to analyze the dynamics of actin in conjunction with the dynamics of calcium signals. Actin dynamics throughout differentiation showed a rhythmic character, localized mostly in processes, with changes in scale associated with differentiation. Furthermore, actin dynamics impact ionic dynamics, with an increase in the frequency of calcium bursts accompanied by a decrease in cell-cell correlations when actin dynamics is inhibited. This impact of cytoskeletal dynamics on cell-cell coupling and ionic neural cell signaling suggests that information flow in the brain may be able to harness both biomechanical and electrical/ionic excitability.

cell biology↗

bioRxiv2022

Enabled primarily controls filopodial morphology, not actin organization, in the TSM1 growth cone in Drosophila

Ena/VASP proteins are processive actin polymerases that are required throughout animal phylogeny for many morphogenetic processes, including axon growth and guidance. Here we use live imaging of morphology and actin organization in the TSM1 axon of the Drosophila wing to dissect the mechanism of Ena action. We find that altering Ena activity has a substantial impact on filopodial morphology in this growth cone, but exerts only modest effects on actin organization. This is in contrast to the main regulator of Ena, Abl tyrosine kinase, which has profound effects on actin and only mild effects on TSM1 growth cone morphology. These data suggest that the primary role of Ena in this axon may be to link actin to morphogenetic processes of the plasma membrane, rather than regulating actin organization itself. These data also suggest that a key role of Ena, acting downstream of Abl, may be to maintain a constant filopodial organization of the growth cone, even as Abl activity varies in response to guidance cues in the environment. Summary statementWe dissect the function of the actin polymerase, Enabled, in axon growth by live-imaging of actin dynamics and axon morphology of the TSM1 neuron in its native environment in vivo.

neuroscience↗

bioRxiv2021

Decoding natural astrocyte rhythms: dynamic actin waves result from environmental sensing by primary rodent astrocytes

Astrocytes are key regulators of brain homeostasis, an important physiological process that includes but is not limited to buffering of extracellular K+, equilibrating osmotic gradients, regulating pH, uptake of neurotransmitters, and releasing growth factors - all of which are essential for proper cognitive function. While previous studies have revealed how specific molecular components of the astrocytic cytoskeleton affect the efficacy of these homeostatic processes, none have studied how homeostasis is linked to the excitable systems character of the cytoskeleton. As recently discovered, excitability of the actin cytoskeleton manifests in second-scale dynamic fluctuations and acts as a sensor of chemo-physical environmental cues. Here we find that homeostatic regulation may be more active than previously thought, involving the excitable dynamics of actin in certain subcellular regions, especially near the cell boundary. Our results further indicate that actin dynamics concentrates into "hotspot" regions that selectively respond to certain chemo-physical stimuli, specifically the homeostatic challenges of ion or water concentration increases. Substrate topography makes the actin dynamics of astrocytes weaker. Superresolution images demonstrate that surface topography is also associated with predominant perpendicular alignment of actin filaments near the cell boundary whereas flat substrates result in an actin cortex mainly parallel to the cell boundary. Additionally, co-culture with neurons increases both the probability of actin dynamics and the strength of hotspots. The excitable systems character of actin thus makes astrocytes direct participants in neural cell network dynamics.

neuroscience↗

bioRxiv2020

A polymer gel index-matched to water enables diverse applications in fluorescence microscopy

We demonstrate diffraction-limited and super-resolution imaging through thick layers (tens-hundreds of microns) of BIO-133, a biocompatible, UV-curable, commercially available polymer with a refractive index (RI) matched to water. We show that cells can be directly grown on BIO-133 substrates without the need for surface passivation and use this capability to perform extended time-lapse volumetric imaging of cellular dynamics 1) at isotropic resolution using dual-view light-sheet microscopy, and 2) at super-resolution using instant structured illumination microscopy. BIO-133 also enables immobilization of 1) Drosophila tissue, allowing us to track membrane puncta in pioneer neurons, and 2) Caenorhabditis elegans, which allows us to image and inspect fine neural structure and to track pan-neuronal calcium activity over hundreds of volumes. Finally, BIO-133 is compatible with other microfluidic materials, enabling optical and chemical perturbation of immobilized samples, as we demonstrate by performing drug and optogenetic stimulation on cells and C. elegans.

bioengineering↗